Original article written by Rodrigo Ramirez-Campillo, Jason Moran, Jon Oliver and colleagues.
Frustratingly, limited research out this month specific to rehabilitation. However, an interesting article overseen by Rhodri Lloyd and co. has been published this month – a qualitative review on the programming of plyometric jump training in soccer players.
In my experience, plyometric training is not prescribed as meticulously as traditional resistance training within our athlete’s rehabilitation programmes. Where practitioners often utilise 1RMs and velocity-based training to prescribe very specific loading during resistance training, the same degree of specificity is not applied to plyometric training. This is likely due to lack of high quality research in this field – so this article had the potential to be very informative.
Background
Plyometric training can be prescribed to facilitate improvements in a strength, speed, power and change of direction performance in soccer players. It typically involves actions such as hopping, skipping, bounding, and jumping.
Plyometric training utilises the rapid cyclical actions of muscles, known as the ‘stretch-shortening cycle ‘(SSC), which is a sequence involving an eccentric muscle contraction, followed by a transitional, amortization phase prior to a concentric muscle contraction with a focus on speed of execution and short ground contact times (GCT). Plyometrics are categorised into ‘slow’ (> 250 ms) and ‘fast’ (<250 ms) activities based off the GCT of each repetition.
Plyometric exercise is deemed a high intensity training method that places significant stress on the muscle-tendon unit. It is for this reason; it does not often feature until the middle and later stages of rehabilitation programmes following musculoskeletal injury. Various clinicians have developed continuum models, that detail the differing types of plyometrics along progressive complexities (see Lachlan Wilmot’s excellent article on Sportsmith).
However, despite the publication of a considerable volume of plyometric training literature, very few studies have attempted to evaluate the optimal training parameters to ensure positive performance adaptations, such as duration, frequency, volume, intensity, type of exercise, recovery, progressive overload, or the type of surface.
Ramirez-Campillo et al.,[1] identified that the most recent systematic reviews surrounding plyometric jump training in soccer with and without meta-analyses include only randomized controlled trials. Such a research design can be logistically difficult to conduct in highly trained athletes and could, therefore, exclude much of the evidence available in soccer athletes. In this scenario, the authors believed a qualitative review would add additional insight into the field of plyometric training by capturing smaller studies and case studies, in addition to the large systematic reviews.
What the authors did
The aim of the article was therefore, to describe and summarise the published scientific literature surrounding jump training in soccer players. Included studies were those interventions, of three or more weeks duration, which included jump training exercises as a primary component, individually or embedded into a wider training program. 90 studies were eligible for inclusion.
What the authors found
The authors looked to summarise their qualitative analysis under the headings of a multitude of training variables.
Duration
The evidence suggests that jump training may induce early adaptations (< 4 weeks) in some outcomes of physical fitness in soccer players with a low training age – these adaptations include improvements in linear sprinting, change-of-direction speed and power. However greater improvements may be expected after longer-term interventions (> 6 weeks). Although the trends in intervention duration are relatively consistent within adult soccer players, no study has compared the relative time-courses of adaptations in adult soccer players’ during a plyometric training programme.
Frequency
The mean training frequency was two sessions per week, although this also ranged from one to six sessions per week. Few studies in soccer players have investigated the effects of different jump-training frequencies on athletes’ physical fitness. Overall, it seems that training frequency (e.g., one versus two sessions per week) does not affect physiological adaptations in soccer players, and volume of training may appear to be the more important training variable.
Type of jump
Unsurprisingly, vertical jump training has a greater impact on physical fitness outcomes with a greater vertical component (e.g., vertical jump), while horizontal jump training may have a greater impact on physical fitness outcomes with a greater horizontal component. However, it was also observed that horizontal jump training was at least as effective as vertical jump training at enhancing vertical performance, suggesting that horizontal jump training might be a more efficient method for enhancing multi-vector performance for soccer players.
Additionally, the type of muscle action (e.g., full stretch-shortening cycle vs. concentric only movement; fast vs. slow stretch-shortening cycle), may also affect the adaptations of soccer players to jump training, with, for example, fast stretch-shortening cycle jump drills exerting a greater effect on the latter stages of a linear sprint and slow stretch-shortening cycle jump drills on the earlier stages.
Total number of jumps
Overall, from the best available evidence (randomized controlled studies), prescribing between 132-236 jumps per week, as a training volume, seems to be effective in improving soccer player’s physical fitness in programmes between 6-8 weeks. There was no significance in improvements based on which end of the this range was prescribed.
Intensity
It was apparent there was no consensus from the studies regarding a clear evidence-based definition of jump training intensity for different jump exercises.
Recovery timeframes
No study involving adult soccer players has addressed the effects of different inter-repetition or inter-set rest intervals on subsequent physical fitness adaptations. This is a key issue that merits further attention.
Progressive overload
Although progressive overload may not be needed in the short-term (e.g. ≤7 weeks), some form of progressive overload would likely be needed during longer-term interventions in order to induce ongoing adaptations in soccer players. This might include resistance bands or weighted vests.
Type of surface
The type of training surface used for jump training may affect the speed of the stretch shortening cycle that is performed, potentially leading toward different adaptations. It was somewhat surprising therefore, that the surface type was not clearly reported in 60% of the included studies. The studies it was reported in, a quantifiable measure of ground hardness was not reported, making it difficult to compare outcomes between studies. Future studies may devote further attention to these potentially relevant aspects of jump training prescription among soccer players.
Limitations
Despite the authors best interests to improve our understanding of the optimal dose for prescribing plyometric training in soccer players, unfortunately it is an area of training that is under researched. This may be because plyometric training prescription is currently perceived as an “Art’ in our industry, as opposed to a hard science – especially when compared to other training methods such as weight training. In the future, practitioners and researchers working within this field may consider a consensus paper to improve the consistency of terminology and quantification of plyometric jump variables. This in tern may help us to improve the reliability and comparability of of future randomised control trials and case studies.
What this means for practitioners
- Plyometric training prescription over 6-8 weeks, with 1–2 sessions per week, with a dose of 80 jumps per session or 140–240 per week, using near-maximal or maximal effort intensity and proper technique, with progressive overload helps to elicit positive physical performance adaptations.
- Research is extremely limited with regards to the prescription of plyometric training. Common sense must prevail, and if objective monitoring of physical performance markers demonstrates appropriate trends, then this indicates that the dose of plyometric training is likely to be sufficient. When positive adaptation starts to slow down, training parameters such as the ones mentioned above should be progressively overloaded to further performance improvements.
Recommended resources
Podcast – Plyometrics and jump training; progressions, regressions and recovery circuits – Boo Schexnayder
Article – Implementing the plyometric continuum to individualise jump and land training – Lachlan Wilmot